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ItemSound sensing B.A.T.S. - Biodegradable acoustic triboelectric nanogenerator sensors(Georgia Institute of Technology, 2024-04-15) Verma, Harsh KumarTwo of the prominent challenges facing modern development of electronic devices are minimizing their power requirements and simplifying the disposal processes. Recent developments in self-powered energy harvesters such as triboelectric nanogenerators (TENGs) have been extensively focused on the use of more environmentally sustainable materials to minimize the environmental impact while being able to harvest energy from the environment. In this thesis, I have investigated 3 different versions of biodegradable triboelectric nanogenerators for acoustic energy harvesting, referred to as biodegradable acoustic triboelectric nanogenerator sensors (BATS). To study the negative layer, I use a tribonegative biopolymer, poly (L-lactic acid) and compare the voltage outputs of the device to traditional materials such as FEP. These results indicated good usability of PLLA based BATS, albeit an order of magnitude lower signal than for FEP based BATS. I also examined how the polymer crystallinity and volatile content in the PLLA films impacts the performance. To study the positive layer, I selected silk fibroin as a tribopositive biopolymer. Variation in voltage output was observed and correlated to changes in drying temperature and the water uptake of the polymer, demonstrating the dependence of the TENG performance on the dynamic behavior of the biopolymers and the environmental conditions. Lastly, I used a contact separation mode for the TENG and examined the combined effects of the triboelectric biopolymers PLLA and silk fibroin on the TENG performance. A shift in the resonant frequency was observed in these devices over time due to the hygroscopic property of both PLLA and silk fibroin. As in the previous cases, the reduction in voltage was observed and correlated with the reducing residual solvent in the films over time. Overall, residual solvent after processing and water absorption, measured by changes in the volatile content of the polymer, were found to be a major factor significantly affecting the properties of the triboelectric layers. Optimizing the processing conditions and the solvents used for these polymers is crucial, as this not only affects their triboelectric property but also, the changes in TENG performance over time.
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ItemIn-situ Polymerization of Methacrylate based Solid Polymer Electrolyte for Solid State Lithium-ion Batteries(Georgia Institute of Technology, 2023-05-03) Chandra, VismayIn the wake of global transition to renewable energy, the demand for energy storage devices has grown exponentially. With electric vehicles (EVs) becoming mainstream, energy dense lithium-ion batteries (LIBs) are the need of the hour. Conventional liquid electrolyte batteries for LIBs may pose a safety hazard due to the use of flammable organic electrolytes with high vapor pressure. Solid state batteries (SSB) may become a solution to this problem if they mitigate the flammability issue and offer sufficiently high energy and power densities required for applications in the electric mobility sector. Conventional methods of processing solid polymer electrolytes (SPEs) and their incorporation into LIBs involve fabricating the electrode(s) and the separator membrane separately. These methods are heavily reliant on toxic solvents and are time and energy intensive processes, which makes a hurdle to commercialization. This thesis employs in-situ polymerization process, which is a one-step process of infiltration of SPE precursors into LIB stack followed by the polymerization and formation of the SPEs. Eliminating the use of solvents and reducing fabrication time makes this technique more attractive for a commercial deployment. A novel SPE is being explored in this thesis. The synthesis of the polymer has been explained and characterizations have been performed to understand thermal and electrochemical stability of the SPE. Systematic studies have been performed to investigate the evolution of resistance and stability of the solid electrolyte interphase (SEI) in contact with electrodes. Finally, the long-term cycling and rate performance of the SPE incorporated into commercial battery materials, such as lithium iron phosphate (LFP) and lithium titanate (LTO) have been evaluated.
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ItemOperando Characterization of Lithium-Ion Batteries using Lab-Scale X-ray Emission/Absorption Spectroscopy(Georgia Institute of Technology, 2023-05-02) Krishnan, AbiramTracking changes in the electronic structure of target elements is crucial to investigate the nature of redox reactions occurring in battery electrodes. Core-hole characterization techniques such as X-ray Emission Spectroscopy (XES) and X-ray Absorption Fine Structure (XAFS) perform this role well through the generation/quenching of core holes in the sample. Laboratory-based core hole x-ray spectroscopy techniques have recently gained popularity as they are more accessible and provide energy resolution close to that of a synchrotron source. In this study, the use of a lab-scale XAFS/XES to investigate the change in the electronic structure around transition elements present in electrode materials for lithium-ion storage is explored under operando conditions. This enables real-time monitoring of chemical shifts resulting from changing electrode potential. The relationship between energy shifts and oxidation/spin state is obtained using K-edge XANES and Kβ1,3 XES measurements of transition metals present using reference compounds. This relationship is utilized to predict the change in chemical environment during the cycling of cathode/anode materials for energy storage. Additionally, the spin sensitivity of Kα and Kβ fluorescence is utilized to explore the magnetic behavior of LCO cathodes in the first 10% of lithium removal along with K-edge XAFS for oxygen and cobalt to investigate local and electronic structure changes.
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ItemFabrication and Characterization of low tortuosity cathode for Sodium-ion batteries(Georgia Institute of Technology, 2023-05-02) Jakhar, RishikaSodium-ion batteries (SIBs) are an attractive alternative to lithium-ion batteries (LIBs) given sodium’s (Na) abundant availability, lower cost, and comparable energy storage characteristics. There is an increasing impetus to increase the energy densities and specific energies of SIBs. One of the ways to achieve this is to produce thicker electrodes with higher areal mass and capacity loadings in order to reduce the relative weight and volume fractions of inactive SIB components, such as current collectors and separators. Unfortunately, fabricating thicker electrodes by conventional slurry-casting methods presents two challenges – (i) avoiding the loss of mechanical strength and (ii) retaining fast ion transport within thick electrodes. In our proof-of-concept studies, SIB cathodes were fabricated using a phase inversion technique to be free-standing, exhibit over 100 µm thickness and possess vertically aligned pores. The electrochemical performance of such electrodes was investigated by studying their charge-discharge (C-D) profiles at different current densities and conducting cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements in half cell configurations. The effects of electrolyte composition and solid electrolyte interphase (SEI) additives were additionally investigated in symmetric cell configurations. The performance characteristics attained suggest a promise of this approach for a broad range of SIB and other battery chemistries. Further work on optimizing the pore shape, pore size distribution and pore volume is expected to further boost cell performance.
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ItemEnhancing The Properties Of Copper Foam Wicks Using Graphene Coatings For High-Performance Vapor Chambers And Heat Pipes(Georgia Institute of Technology, 2023-05-02) Moss, James AlexanderWith the increasing thermal densification of consumer and portable electronics, the implementation of two-phase capillary flow-driven structures (e.g., vapor chambers, heat pipes) in thermal management has grown exponentially. These structures utilize the latent heat of evaporation of a working fluid along with the thermal and capillary capabilities of a wick to efficiently mitigate hot spots through heat spreading; however, material development for improved thermal capabilities of these two-phase wick systems is underdeveloped for what is needed in future electronic packages. As a result, this research explores the use of conformal graphene coatings deposited on open-cell copper foams to enhance their properties and performance. A controlled chemical vapor deposition process was utilized to conformally coat monolayer graphene on different copper foam densities with varying pore sizes and 3D connectivity. The thermal, electrical, and mechanical properties were then characterized before and after the graphene was deposited to understand the effect of the coating on the foams. Permeability and wettability were also evaluated to understand the potential of the coating on high-performance wicks. An electroless copper deposition process was then developed to deposit a conformal intermediate copper layer that could separate parallel graphene networks with further sequential deposition of alternating graphene and copper layers. This thesis reports the resulting improvements in wick properties and performance from graphene coatings, establishing this method as a promising pathway for compact and highly efficient in-package heat spreading solutions, and provides design guidelines to maximize benefits from this material innovation with considerations of ease of processability and cost.
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ItemInvestigating the impedance characteristics of insulating thin film capacitors and Conducting thin film inductors for advanced electronics applications(Georgia Institute of Technology, 2023-05-01) Nellithala, Dheeraj BabuThin film capacitors and inductors have garnered significant research interest due to their compact size, lightweight nature, versatile integration capabilities, and superior performance characteristics in high-frequency applications. Researchers have been exploring novel materials, deposition techniques, and device architectures to enhance the efficiency and reliability of these essential components. Advancements in material synthesis, such as atomic layer deposition and chemical vapor deposition, have produced highly uniform and conformal thin films with superior electrical properties. Furthermore, developing sophisticated analytical techniques, including impedance spectroscopy, UV-vis spectroscopy, and X-ray diffraction, has facilitated a more in-depth understanding of the complex relationships between film composition, structure, and electrical behaviour. This research comprehensively investigates the impedance properties of insulating thin film capacitors, explicitly focusing on silicon dioxide (SiO2), aluminium oxide (Al2O3) materials, and conducting thin film inductors. The study examines the influence of critical parameters that affect the measurements, such as film thickness, the distance between the electrodes, electrode types, and equipment factors, on the overall performance of these devices. The thin films were also characterized using Ultraviolet-Visible (UV-Vis) spectroscopy and X-ray Diffraction (XRD) to verify their composition, thickness, and degree of crystallinity. For the insulating films, the results revealed a dependency of the impedance characteristics on film thickness but not pad distance. For the thin film inductors, optimizing the measurement cables enabled more accurate measurements of the resistance by minimizing the influence of parasitic components on the measured impedance.